Ever since water filters were researched, developed and widely used unceasingly, most of them still use a single and replaceable filtration core, which is an integrated unit composed of different filtration materials. Although traditional water filter requires only the change of a new filtration core and the cleaning of the container where the filtration core is put, its short filtration distance makes the process of filtration insufficient. Besides, filtration materials with longer life-spans must be replaced at the same time when those of shorter life-spans, all of them in the same unit, are damaged and must be replaced, thus causing a waste of energy resources and money. As a result, water filters with the so-called "layer-piling" structure is introduced to avoid unnecessary waste.